These advertising IDs allow buyers to match their data about users to the user behind an impression received from an exchange. This promotes effective remarketing, frequency capping, and conversion tracking on DoubleClick Ad Exchange inventory. In addition, it enables advertisers to more effectively measure the performance of their campaigns through improved tracking and attribution, which will unlock new monetization opportunities for publishers.

The user turns on limit ad tracking – LAT (iOS) or opts out of interest-based ads on Android devices.

To better inform your audience about how advertising IDs from their device will be used, we require that publishers using mobile advertising IDs comply with the disclosure requirements in the "In-App Ad Remarketing" provisions of the Google Ad Manager Partner Guidelines.

With the release of iOS 6, Apple replaced its Unique Device Identifier (UDID)(which allowed developers and marketers to track activity on the phone, such as app purchases, delivering push messages, or any other activity unique to that iPhone) with a new, privacy friendly, user resettable Identifier for Advertising (IDFA).